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Case of the Week #61

Clinical history

At a well child checkup, a 15 month
old asymptomatic boy was noted to have a large, right upper quadrant abdominal
mass. CT scan showed a large hepatic mass extending to the level of the iliac
crest. Laboratory testing showed an elevated AFP at 1398, and the clinical
impression was hepatoblastoma.

The images show branching bile ducts
without atypia in a loose, myxoid stroma with myofibroblast-like cells, dilated
vessels and lymphatics. At low power, it may resemble fibroadenoma. At high
power, normal appearing hepatocytes are often present. There is usually extramedullary
hematopoiesis, and the bile ducts may have a mesenchymal collar. No atypia or
tumor giant cells are present.

Mesenchymal hamartoma was previously
called cavernous cystic hamartoma, lymphangioadenomatoid tumor and benign
mesenchymoma. It is typically an asymptomatic pediatric tumor, with 75%
occurring before age one year and 2/3 occurring in males. It comprises 8% of
all pediatric liver tumors. The AFP is typically normal or minimally
elevated, although occasionally it is markedly elevated.

These tumors range from 5-23 cm, and
are typically solitary and well circumscribed. They often have fluid filled
cysts (see figure
1), and become fibrotic with age. There is usually no necrosis,
hemorrhage or calcification.

Mesenchymal hamartomas typically have
benign behavior, although they rarely transform to embryonal sarcoma (Pediatr
Dev Pathol 2001;4:482). Treatment consists of excision,
which is curative, but associated with high mortality, particularly with very
large tumors.

In adults, the tumors are more
fibrous and less myxoid, and extramedullary hematopoiesis is rare. Liver
transplantation may be necessary (J
Clin Pathol 2006;59:542)